Three picture naming experiments are reported which examine the
relationship between the apparent inhibition of a response on one trial,
and naming latency on the subsequent trial. The design of each
experiment involves the presentation of prime and target pairs, either
presented in succession (Lag 1 condition), or separated by two
intervening unrelated trials (Lag 3 condition). A control condition is
also included. In Experiment 1, a speeded picture naming task is used,
and naming errors are analysed. Target pictures are misnamed at above
chance rates with the name of the semantically related prime picture in
the Lag 3 condition. In contrast, these prime-related errors do not
occur in the Lag 1 condition, suggesting a brief inhibitory effect. If
primes are briefly inhibited, then target naming larencies immediately
following a related prime should be quicker than target larencies in the
Lag 3 condition. Experiment 2 confirms this pattern of results, using
exactly the same stimuli and design, but standard nam ing instructions.
Experiment 3 examines whether the inferred inhibition is the result of a
self-inhibitory mechanism, using a repetition priming paradigm. If Lag 1
prime representations are self-inhibited, then facilitatory effects from
prime/target repetition should be stronger in the Lag 3 condition, than
in the Lag 1 condition. The data from Expt 3 were not consistent with
this prediction. Taken together, the results of the three experiments
suggest that a brief inhibitory effect occurs after retrieval of an
object name, and that the inhibition may be accomplished by mechanisms
other than self-inhibition.

A number of different studies have shown that object name retrieval
can be impaired when the names of other objects from the same semantic
category have earlier been retrieved (Brown, 1981; Kroll & Stewart,
1994; Vitkovirch & Humphreys, 1991; Wheeldon & Monsell, 1994).
For example, Wheeldon and Monselt (1994) have shown that retrieving an
object name from a definition can slow picture naming latencies when a
semantically related picture is presented three or more trials later.
Vitkovitch and Humphreys (1991) found that when participants named a
block of target objects under speeded naming instructions, they
frequently made errors which corresponded to semantically related primes
which had been named in a previous block (perseverative errors). These
results fit generally with the conclusion in the literature that object
name retrieval is subject to semantic competition, shown by a number of
other paradigms, such as picture--word interference tasks, (e.g. Glaser
& Glaser, 1989; Srarreveldt & La Heij, 1995) or b y post-cue
naming techniques (Humphreys, Lloyd-Jones, & Fias, 1995). The
finding that an earlier named object interferes in particular with
target name retrieval is thought to be due to the strengthening of an
aspect of the prime's representation in memory, making it more
likely to be sampled as a candidate response before the target name
(Brown, 1981), or making it an especially strong competitor when it is
activated, along with other competitors, in parallel with target
representations (Humphreys, Riddoch, & Quinlan, 1988; Wheeldon &
Monsell, 1994).

More recently, we have found that there is a distinct pattern
apparent in the incidence of perseverarive errors. Vitkovitch, Kirby,
and Tyrrell (1996) presented a sequence of related objects, and examined
the perseverative naming errors as a function of lag between error and
earlier response. While errors relating to responses at least four
trials earlier (Lag 4) were evident at above chance rates, there was an
absence of errors relating to the immediately preceding trial (Lag 1),
and this was below chance rate. Very similar results have been found by
Campbell and Clark (1989) in their analysis of errors made during the
retrieval of answers to simple arithmetic problems (6 x 3, 7 x 9 etc).
In line with Campbell and Clark (1989), we interpreted the negative
error priming (i.e. absence of Lag 1 errors) as indicative of a brief
inhibitory effect. Houghton & Tipper (1994) have recently referred
to inhibition as a state of suppressed responsiveness, and it is in this
sense that we use the term here. Once the inhi bitory effect is removed,
the excitatory influences which cause the perseverative errors are
revealed in above-chance error rates at longer lags (positive error
priming).

There is increasing use of the metaphor of inhibition in the
literature on cognition. For example, Tipper and Driver (1988) suggested
that inhibitory processes can account for a negative priming effect
found in a selective attention paradigm. Other areas of cognition which
have implicated inhibitory processes are language production (e.g. Dell
& O'Seaghda, 1994), episodic retrieval (Anderson & Bjork,
1994), and language comprehension (Gernsbacher & Faust, 1995).
Houghton and Tipper (1996) have also recently suggested that inhibitory
mechanisms may be useful in sequential tasks generally, to prevent
reiteration of a previous response.

There are several mechanisms by which such inhibition might be
achieved. Lateral inhibition from each node to others at a given level
of representation has long been a feature of interactive activation
models of stimulus recognition (McClelland & Rumelhart, 1981).
Lateral inhibition may function to reduce the kind of interference that
is caused by parallel activation of representations other than those of
the target, as in the examples of semantic competition given above
(Humphreys et al., 1988; Wheeldon & Monsell, 1994). Another possible
means by which inhibition could be implemented is by representational
nodes inhibiting themselves. This might be particularly useful in
sequential tasks, and in language production in particular. Arbuthnott
(1995) has presented a possible model of such self-inhibitory
mechanisms. She also raises the issue of whether such inhibitory
mechanisms are largely automatic or whether they can be modified as a
result of strategic processing. A further possibility is that active
suppr ession can operate in the absence of hard-wired inhibitory
structures.

The three experiments reported here extend our previous work on
inhibition during object name retrieval. The studies on naming errors
(Vitkovitch & Humphreys, 1991; Vitkovitch et al., 1996) and naming
latencies (e.g. Wheeldon & Monsell, 1994) seem to complement each
other in showing semantic competition from earlier object naming trials.
Campbell (1990) has examined the relationship between the apparent
inhibition of representations on one arithmetic trial, and latencies to
retrieve answers on the next trial. As yet, we have not examined
latencies in relation to inhibition during object name retrieval.
Vitkovitch et al. (1996), for example, looked at lag effects only in
terms of the errors which emerged naturally as a result of speeded
naming of a series of related pictures. The design precluded an analysis
of response latencies in relation to lag. In the experiments below, we
use a design similar to that employed by Wheeldon and Monsell (1994),
and this enables us to manipulate the lag between related prime and
target pictures and examine latencies. Experiment 1 replicates our
previous work on detecting inhibition through analysis of error patterns
using this different experimental design, and Expt 2 provides converging
support for the presence of inhibition on prime trials through an
analysis of naming latencies on target trials. Experiment 3 represents a
preliminary investigation of the mechanism by which any such inhibition
is achieved. It uses a repetition priming paradigm to examine whether
effects are explained by a self-inhibitory process.

EXPERIMENTS 1 AND 2

In Expts 1 and 2, participants were asked to name a series of
pictures, and we explored the relationship between the apparent
inhibition of a particular response (indicated previously by analysis of
naming errors) and naming latencies to a subsequent semantically related
target trial. If a potential competitor to the target has been
temporarily inhibited on the immediately preceding trial, then it
follows that target naming latencies should be faster when a related
prime and target are successive than when they are separated by a number
of trials, when inhibition is no longer present. Consistent with this
argument, Campbell (1990) found that the retrieval of answers to
arithmetic problems was facilitated after supposed inhibition of a
competitor.

One problem is that it can be difficult to examine both naming
latencies and errors simultaneously. Speeded picture naming instructions
do increase the error rate, but this can be at the expense of reliable
or informative latencies. Instructions to name as quickly but as
accurately as possible (standard naming instructions) clearly give
better latency estimates, but it is not always the case that errors are
sufficient for analysis. For these reasons, in Expt 1, speeded naming
instructions were used, and errors were the main dependent variable. In
Experiment 2, normal naming instructions were used, and naming latencies
were the main dependent variable. The second dependent variable was
noted in each case. Both experiments used the same stimuli and design,
and so they are reported together.

In a design similar to one employed by Wheeldon and Monsell (1994),
related primes and targets were presented, either in succession (Lag 1
condition), or separated by two intervening unrelated trials (referred
to as Lag 3 condition, for consistency with our earlier work on lag
analyses). A control condition was also included. All stimuli were
pictures of objects. Previous work in our laboratory has indicated that
inhibition has been removed sufficiently after a Lag of 3 for
perseverative errors to occur as a result of the residual activation
which remains in prime representations (Vitkovitch & Rutter, 2000).
We predicted, therefore, that under speeded naming instructions (Expt
1), prime-related errors for targets under the Lag 1 condition should be
significantly lower than in the Lag 3 condition, due to inhibition of
the prime representations in the former condition. The control condition
provided a baseline estimate of the occurrence of these same types of
errors in the absence of a related prime. The Lag 3 error rate should be
significantly higher than the control condition, while the Lag 1 error
rate should be below that of the control condition. In Expt 2, in line
with the semantic priming studies which examined target latencies
(Wheeldon & Monsell, 1994), target pictures in the Lag 3 condition
should have longer latencies than in the control conditions, as a result
of specific interference from the prime. However, if prime
representations are very briefly inhibited, then target picture naming
latencies in the Lag 1 condition should be significantly less than in
the Lag 3 condition. It is not clear whether latencies in the Lag 1
condition will also be longer than the control condition, because this
could depend on whether all or only some aspects of the representation
of that prime object are inhibited. Campbell (1990), for example, found
latencies actually to be quicker in the related condition than in the
unrelated condition.

Method

Participants

Two groups of 24 students from the University of East London
volunteered to take part in these experiments. All had English as their
first language, and all reported normal or corrected eyesight. In both
experiments, age ranged from 18 to 45 years, and the samples were
approximately two-thirds female. In Expt 1, one participant who made no
naming errors (apart from a Pass' response) was replaced.

Design and stimuli

A total of 36 pairs of related prime and target pictures were
selected from the Snodgrass and Vanderwart (1980) set, from a range of
semantic categories (e.g. animals, musical instruments, vehicles,
clothes, household items, tools, fruits, vegetables). On the basis of
inspection of naming errors from previous research, the prime was
selected so that it appeared to be a strong competitor for the target.
Examples of primes and targets are bus and lorry, guitar and violin,
aeroplane and helicopter. The primes and targets were selected so that
the different pairs did not interfere with each other. In addition to
the prime and target, two unrelated filler pictures were selected, so
that primes and targets were presented in sequences of four pictures.
The lag between prime and target was manipulated, leading to two
experimental conditions. In the Lag 3 condition, the two unrelated
filler pictures intervened between prime and target (e.g. aeroplane,
filler, fillet, helicopter). In the Lag 1 condition, the target imm
ediately followed the prime, and the two unrelated fillers preceded the
prime (filler, filler, aeroplane, helicopter). A third control condition
was included, in which the target was presented without any related
prime, but instead an extra unrelated picture was included (filler,
filler, filler, helicopter). Thus, the sequences of four stimuli
constituted one trial, although this was not apparent to participants.
The 36 pairs of related prime and targets and fillers were divided into
three lists of 12 pairs, such that there were an equal number of
exemplars from each category in each list. The lists were rotated across
the three conditions, so that, across the participant group, each target
picture appeared under each of the three conditions an equal number of
times. No stimulus ever appeared more than once for each participant.

Procedure

The pictures were digitized and presented on a Macintosh computer
using the Psychlab software package (Bub & Gum, 1990). Pictures were
presented as black outline drawings within a light grey window. The
picture disappeared from the screen after 500 ms and, in Expt 1, an
auditory buzzer sounded at this point, to indicate a deadline which
participants should try to beat. All participants were asked to name the
pictures, but participants in Expt 1 were encouraged to try to do so
before they heard the buzzer. They were advised nor to be concerned
about any errors, since speed was more important than accuracy.
Participants in Expt 2 were simply asked to respond as quickly but as
accurately as they could. All participants wore a neckband with a
microphone, which triggered a millisecond timer. After each response,
there was a 4 second interval before the next picture was presented. The
pictures were presented in a different random order to each participant,
and the experimenter noted any hesitations, naming errors, and equipment
failures. Participants were given four practice trials (12 stimuli)
before the start of the experiment. They were informed that they could
stop the experiment at any point if they so wished.

Results

The results are organized so that the analyses of errors are
presented first for both experiments, followed by analysis of naming
latencies.

Analysis of errors

Naming errors were classified as prime-related when they
corresponded to the related prime. in the control condition, a
prime-related error was scored if the target error corresponded to the
related (though unseen) prime for that specific target. The percentage
of naming responses which were prime-related errors are presented for
each condition in Table 1. There were also a number of errors which
reflected the names of other exemplars from the same semantic category
as the target, and for comparison purposes, the percentage error rates
for these 'non-prime-related errors' are also presented in
Table 1. Other inaccurate responses included the use of superordinate
terms and the occasional 'Pass' response. There were very few
unrelated responses (less than 1%).

The prime-related errors from Expt 1 were analysed using
non-parametric statistics, because the data for the Lag 1 condition were
not, nor were they expected to be, normally distributed. The Friedman
analysis of variance by ranks indicated a significant difference across
conditions, [[chi]sup.2](2) = 9.15, p 9.15, p = .01. Wilcoxon tests
(one-tailed) were used for the follow-up comparison tests. As predicted,
there were more prime-related errors in the Lag 3 condition than in the
Lag 1 condition, Z = 3.09, p [less than] .01. For the two comparisons
against the control condition, the alpha level was set at .025. There
were significantly more prime-related errors in the Lag 3 condition than
the control condition, Z = 2.43, p [less than] .01. The difference in
error rate between Lag 1 and control condition approached significance,
Z 1.60, p = .05.

The non-prime-related errors were analysed similarly using the
Friedman test. Although there was some reduction in error rate in the
Lag 3 condition, there were no significant differences between
conditions, [[chi]sup.2](2) = 1.75, p [greater than] .05.

The prime-related error rare was low in Expt 2. Once again, though,
a reduced error rate for the Lag 1 condition relative to the other two
conditions is evident. Although the Friedman analysis showed no
significant difference between the three conditions ([[chi].sup.2](2) =
1.71, p [greater than] .05), the planned Wilcoxon test indicated that
the difference between Lag 3 and Lag 1 conditions was significant, Z =
1.77, p [less than] .05, (one-tailed test). The comparisons of each
experimental condition against the control conditions did not reach
significance (p [greater than] .025).

The non-prime-related errors failed to show any difference across
conditions, ([[chi].sup.2](2) 0.44, p [greater than] .05.

Analysis of naming latencies

Median response latencies were calculated for each participant for
each condition, excluding hesitations, or failures of the timing
mechanism. Latencies were also excluded for any trials on which either
the target or the prime had been misnamed. Table 1 gives the mean of the
median response latencies for each condition for both Experiments.
Unfortunately, latencies were not recorded on all trials for three
participants in Expt 1, and so latencies were not available for these
individuals. A further (outlier) participant was also eliminated due to
very long latencies.

In all experiments, mean naming latencies were also calculated for
each participant, but the results of these analyses (and any data
transformations) will only be presented where these differ from analysis
of median latencies.

A one-factor repeated-measures ANOVA indicated no significant
differences in median latencies across conditions in Expt 1, P1(2, 38) =
1.03, p [greater than] .05, MSerror = 6427. However, in Expt 2, a
significant difference between conditions was found, F1(2, 46) = 6.98, p
[less than] .01, MSerror = 9704. The planned comparison of Lag 3 and Lag
1 latencies was significant, t(23) = 2.89,p [less than] .01, one-tailed,
with longer target latencies in the Lag 3 condition. Comparisons of each
experimental condition against the control condition, using
Dunnett's modified t test, confirmed that latencies were longer in
the Lag 3 condition than the control condition (p [less than] .01,
one-tailed). There was no difference between the Lag 1 latencies and
control latencies (p[greater than] .05). Analysis treating items as a
random factor confirmed this pattern of results, P2(2, 68) = 7.67, p
[less than] .01, Mserror = 13317. One item (tiger) was excluded from the
analysis because there were insufficient latencies due to a high error
rate. The differen ce between Lag 3 and Lag 1 condition was significant,
t(34) = 3.83, p [less than] .01, one-tailed. Comparisons against the
control condition (Dunnett's test) again indicated a difference
between Lag 3 and the control condition (p [less than] .01, one-tailed
test), but no difference between Lag 1 and control condition (p[greater
than] .05).

Discussion

The data from Expts 1 and 2 show a specific interference effect
from semantically related prime pictures which have been presented three
trials earlier. In Expt 1, the prime-related error rate in the Lag 3
condition was significantly higher than the control condition, and in
Expt 2, Lag 3 target picture naming latencies were slower than the
control condition. The analysis of latency data from Expt 1 did nor
reveal any significant differences between the Lag 3 and control
conditions. As noted earlier, this was not unexpected. In both
experiments, however, the pattern of data for the secondary dependent
variables was consistent with the results just reported, although in
Expt 2 there was only a very slight rise in the Lag 3 prime-related
error rate relative to the control condition. The most straightforward
interpretation of the results for these two conditions across the
experiments is that in the speeded naming condition, participants
respond before they can eliminate the strong competition from the prime,
an d so prime-related errors emerge in the Lag 3 condition. In Expt 2,
where it is clear that they take more time to respond and make fewer
errors generally, participants rarely make prime-related errors in the
Lag 3 condition because they spend additional time in overcoming the
competition from the prime. The semantic interference effect evident in
the Lag 3 condition replicates other results reported in the literature
which indicate that name retrieval involves competition from other
exemplars from the same semantic category (e.g. Wheeldon & Monsell,
1994).

In both experiments, the prime-related error rate was significantly
lower in the Lag 1 condition than the Lag 3 condition. Lag 1
prime-related error rate was also lower than the baseline estimate
provided by the control condition, although this comparison of
prime--related errors only approached significance in Expt 1; it may be
difficult to establish a significant difference between these two
conditions because of a floor effect. The differential prime-related
error rate as a function of lag between prime and target is entirely
consistent with our previous work on errors (Vitkovitch etal., 1996;
Vitkovitch & Rutrer, 2000). These error data suggest that there may
be a temporary inhibitory influence directed at prime representations
which immediately precede a target, which limits the interfering
potential of the prime. The latency data in Expt 2 are consistent with
this interpretation. Earlier, we argued that if the potential for the
prime to act as a competitor has been reduced in the Lag 1 condition,
then naming latencies in the Lag 1 condition should be faster than
latencies in the Lag 3 condition. This result was confirmed in Expt 2.
Furthermore, naming latencies in the Lag 1 condition did not differ from
the control condition.

There is, however, an alternative explanation for the reduced
interference effects in the Lag 1 conditions. Wheeldon and Monsell
(1994) similarly found that when related prime definitions and target
pictures were separated by two intervening unrelated trials, the
interfering effect was stronger than when prime definition and target
picture followed each other. They suggested that at a Lag of 1, two
counteracting influences were in operation. The interference effect from
the prime was reduced, not because of suppression, but because of the
prime resulting in a brief facilitatory effect. Facilitatory priming
effects between related prime and target pictures have frequently been
found in the literature (Bajo, 1988; Carr, McCauley, Sperber, &
Parmalee, 1982), and the facilitation is usually explained by reference
to automatic spreading activation within semantics, allowing
pre-activation of target representations. Usually, though, the interval
between prime and target is relatively short (e.g. less than 1 second ).
However, semantic facilitation could occur at longer time intervals as a
result of more deliberate, controlled processing (Neely, 1977). Thus,
the explanations differ for what appears to be a similar result which
has been found in two paradigms which differ mainly in the presentation
form of the prime (definition or picture).

Given the similarity of the results across these studies, we should
consider whether a facilitatory effect from the related prime in Lag 1
position can explain the current results. Anderson and Spellman (1995)
have highlighted the difficulty in drawing inferences about inhibitory
effects from response latencies in particular. However, an analysis of
errors can help in the present case. The relative incidence of
non-primerelated errors across conditions provides an indication of the
competition from other category exemplars during name retrieval. To
address the facilitatory account of reduced interference effects, we
need to compare the incidence of non-prime-related errors across Lag 1
and control conditions within each experiment. If the reduced Lag 1
interference effects evident in the prime-related error analysis of Expt
1 and the latency analysis of Expt 2 were due to facilitation from the
prime, then the non-prime-related errors should also be reduced in the
Lag 1 condition. In Expt 1, the non-prime-rel ated error rate is at or
just above 5% for both Lag 1 and control conditions, and there was
clearly no significant difference between the two conditions. In Expt 2,
although admittedly the error rate is really too low for meaningful
interpretation (and there were no statistical differences in the overall
analyses), it is again the case that there is a greater decrease in
prime-related errors across control and Lag 1 conditions than there is
in non-prime-related errors. Given that in Expt 1, the reduction in
prime-related errors in the Lag 1 condition relative to the control
approached significance, we maintain that the present data fit better
with the suggestion that the absence of an interference effect from
primes in Lag 1 condition is due to a brief suppression effect directed
specifically at prime representations. We return to discussion of these
two interpretations of reduced interference effects later.

EXPERIMENT 3

There could be at least two mechanisms by which prime
representations are inhibited. One possibility is that the Lag 1 prime,
as a potentially very strong competitor, is subject to lateral
inhibition from the related target itself. Dell and O'Segahdha
(1994) discuss the possibility that lateral inhibition may be
sufficiently dynamic to be directed to the most potent competitor, which
could account for inhibition of an immediately preceding prime trial,
but not one several trials earlier. A second possibility is that prime
representations undergo a brief period of self-inhibition. Arbuthnott
(1995) favours a self-inhibitory account of the inhibition which occurs
in number-fact retrieval, and this also fits well with Houghton and
Tipper's (1996) discussion of the use of inhibition in sequential
tasks.

In the sequential naming task, if the object representation
inhibits itself, rather than receives lateral inhibitory input from
another competing representation, then it follows that there may be some
difficulty in re-activating that same representation when it is
re-presented immediately, in place of a semantically related trial.
Experiment 3 investigates this possibility by examining whether there is
any difference in target picture naming latencies as a result of
retrieving the same name (during a prime trial) either immediately
before the target, or three trials earlier.

There is ample evidence that this kind of repetition priming
actually leads to strong facilitation in retrieving target names (Brown,
Neblert, Jones & Mitchell, 1991; Dean & Young, 1996; Durso &
Johnson, 1979; Ferrand, Grainger & Segui, 1994; Griffin & Bock,
1998 (Expt 1); Mitchell & Brown, 1988; Warren & Morton, 1982;
Wheeldon & Monsell, 1992). One account of repetition priming
suggests that there is a change in activation levels of some (or all) of
the representations which are involved in picture naming, so that there
is a benefit in repeated processing e.g. excitation may remain in
structural representations (Dean & Young, 1996; Warren & Morton,
1982), or there may be a strengthening of the links between lexical
representations (Monsell, Matthews, & Miller, 1992). Facilitation
effects can last over a number of lags, and even over a number of weeks
(Mitchell & Brown, 1988). Therefore, relative to baseline trials, we
would expect some facilitation to occur in trials which repeat stimuli
after two interveni ng stimuli (Lag 3 condition). There is also some
evidence in other studies that facilitation is found when immediate
repetition conditions are compared to control conditions (Arburhnott
& Campbell, 1996; Durso & Johnson, 1979). This does not rule out
the possibility of selfinhibition; suppression may be released when the
same stimulus is re-presented (see, for example, Klein & Taylor,
1994; Neill, Valdes, & Terry, 1995; Tipper, Weaver, Cameron,
Brehaut, & Bastedo, 1991) and/or self-inhibitory influences may be
directed at only part of the prime representation, leaving other aspects
highly activated. What would be of particular interest, however, would
be slower target naming larencies in the immediate repetition condition
relative to the Lag 3 repetition condition (our earlier experiments have
shown that by Lag 3, representations have already recovered from the
effects of inhibition). Such a pattern of results would be consistent
with prime representations undergoing a brief period of self-inhibition.
By cont rast, equivalent Lag 3 and Lag 1 repetition priming effects (or
slightly stronger Lag 1 effects) might be expected if there were no
temporary period of self-suppression.

Experiment 3 uses the same design as the two previous experiments,
although some changes were introduced in an attempt to overcome certain
difficulties inherent in repetition priming studies. The prime stimuli
were presented as definitions, from which the object name had to be
retrieved. Wheeldon and Monsell (1992, 1994) used a method of
alternating definitions and pictures to minimize the possibility of
retrieval of an episodic trace, which can occur when participants detect
similarity between prime and target trial (see Brown et al., 1991; Dean
& Young, 1996; Jacoby, 1983; Monsell, 1991; Neill, 1997; Wheeldon
& Monsell, 1992, for a more detailed discussion of episodic and
other, related accounts of repetition priming). The use of an episodic
trace might be particularly likely when trials are repeated in
succession, and so in the present context, might allow participants to
simply restate the previous name, and possibly by-pass any
self-inhibited representations. Wheeldon and Monsell (1992) suggest that
cha nging the actual form and task requirements for prime and target
would reduce the likelihood that participants would retrieve an episodic
trace, and encourage object name retrieval via access to stored
representations. They argued that the processes involved in retrieving
the name from a definition and naming a picture should overlap at the
stage of activating semantic representations, a stage which is prior to
lexical retrieval.

A second potential problem is that inhibition during sequential
picture naming may be under strategic control, and that participants
either do or do not inhibit a response, depending on whether they
perceive it to be useful for later trials. So, in blocks of trials where
stimuli are frequently repeated, self-inhibitory mechanisms may simply
be abandoned. Arbuthnott and Campbell (1996) have examined whether
negative error priming in arithmetic retrieval is due to intentional
suppression, but did find some evidence for automatic inhibitory
processes. However, in the present case of object naming, we cannot rule
out the possibility that immediate repetition of trials may lead
participants to abandon the use of inhibitory mechanisms which under
other circumstances they make use of.

Arguments for or against self-inhibitory mechanisms would therefore
be more compelling if repetition priming data could be evaluated in the
context of other data which were consistent with inhibitory effects.
Therefore, in Expt 3, we aimed to replicate the reduced semantic
interference effects from Lag 1 primes which were evident in the naming
latency data of Expt 2. We included semantic priming trials in addition
to repetition priming trials.

Experiments which include both repetition and semantic priming
trials are not without their own difficulties, though, and Neumann
(2001) has highlighted research which suggests that strategies induced
by one condition can be applied inappropriately to other conditions,
distorting results or interpretation. In studies of selective attention,
negative priming is apparent when an unattended prime is presented as a
target on a subsequent trial. Positive (facilitatory) priming can also
be found when the attended prime is repeated on the next trial. Neumann
suggests that the inclusion of repeated items in negative priming
studies might allow participants to develop anticipatory strategies,
which would have adverse effects for trials where stimuli are not
repeated. The size of repetition priming effects may depend on the
proportion of repeated trials, and discrepancies across studies may be
due to this. Conceivably, also, the size of negative priming effects may
be influenced by the inclusion of repetition priming trials. Arbuthnott
and Campbell (1996), for example, have suggested that the inclusion of
repeated trials in studies of negative error priming in number fact
retrieval may lead participants to develop 'response
detection' strategies, which might mask negative error priming
effects. As in the episodic retrieval account of repetition priming,
they suggest that participants' awareness of repetition may lead
them to check the last response to see if it matched the requited target
name, and if so, they respond with this answer. Arbuthnott and Campbell
(1996) showed that participants use of the prime is dependent on their
detecting similarity between repeated trials, and mistakenly detecting
similarity in related trials (e.g. 4 X 6, 4 X 8). Using this strategy,
participants would, for some trials, by-pass the usual retrieval of
arithmetic facts from stored knowledge. A strategy such as this would be
likely to lead to occasional errors and longer latencies on trials which
were immediately preceded by primes which cl osely resembled the target
in form, and this is what they found.

Therefore, there does need to be caution in interpreting results
from repetition priming studies, and also those which have both related
and repetition prime conditions. For this reason, Expt 3 represents only
a preliminary attempt to investigate the issue of self-inhibitory
mechanisms. Nevertheless, we considered it worth running a repetition
priming experiment, since the finding of stronger Lag 3 facilitatory
priming effects (relative to Lag 1 effects) would be good evidence for a
self-inhibitory mechanism. There is a difficulty, however, in settling
on an appropriate number of repetition trials; the work by Neumann
(2001) has shown that participants can be biased towards or against
repetition, influencing the results. In the following experiment, we
considered it important to demonstrate inhibitory effects in the
semantic priming trials, and to avoid strategic use of the prime, and so
we aimed to avoid a bias towards repetition. The proportion of
repetition trials relative to non-repetition trials was kep t low. In
the Arbuthnott and Campbell (1996) study, for example, 25% of trials
were immediate repetitions, and negative error priming was evident at
least when primes were dissimilar to targets. In the following
experiment, repetition primes were also presented on approximately 25%
of trials (where trials refers to sequences of four stimuli). Although
the actual number of repetition priming trials was only six for each
condition, repetition priming effects in object naming are generally
robust, and we anticipated that they would be detected with this number
of trials.

To review, relative to the control condition, we expected to
replicate the previous finding of interference from semantically related
definition primes in the Lag 3 condition (Wheeldon & Monsell, 1994),
and to find reduced or no interference effect from related primes in the
Lag 1 condition, suggesting a brief inhibitory effect. If this were
accompanied by reduced repetition priming effects for the Lag 1
condition relative to the Lag 3 repetition priming condition, then this
pattern of latency data as a whole would be consistent with an
inhibitory effect occurring as a result of a self-inhibitory mechanism,
whether automatic or intentional. If, on the other hand, reduced Lag 1
interference effects were found in tandem with equivalent Lag 1 and Lag
3 repetition priming, then this would suggest that inhibition in the Lag
1 semantic trials was accomplished by some mechanism other than
self-inhibition. By contrast, if the inclusion of repeated trials
results in participants abandoning the use of inhibition, or i nduces
strategic use of the prime (e.g. anticipatory strategies or a bias
towards repetition, or retrieval of episodic trace), then we might
expect greater facilitatory priming in the Lag 1 repetition priming
condition relative to the Lag 3 condition coupled with costs for the
semantic priming conditions; in particular, the Lag 1 related condition
would then show stronger interference effects from Lag 1 primes than
from Lag 3 primes.

Method

Participants

A total of 36 volunteers from the same population of students as
those participating in the previous experiments were tested. They met
the same criteria as before.

Design and stimuli

The basic design was as for Expts 1 and 2, in that primes were
either presented in Lag 3 or Lag 1 position, and control conditions were
again incorporated. Unrelated filler stimuli were included as before.
However, in this experiment both repetition priming and semantic priming
were examined simultaneously. All primes were presented as definitions,
from which the object name had to be retrieved. The target was always a
picture. On some trials (approximately 25% - see below), the name
retrieved from the prime definition was the same as the name to be
retrieved from the target picture. However, for approximately 40% of the
trials, the prime was semantically related to the target, as in Expts 1
and 2. The remaining trials were unprimed.

For the Lag 3 condition, the sequence of stimuli was; prime
definition, filler picture, filler definition, target picture (the
target could be either the same or semantically related to the prime).
In the Lag 1 condition, the sequence was: filler definition, filler
picture, prime definition, target picture (again, repetition or
related). The two control conditions (one to allow comparisons with the
related prime conditions, and one for comparisons with repetition
priming conditions) consisted of three unrelated filler stimuli before
the target, with the same sequencing of definitions and pictures.

Some changes were made to the actual lists of prime and target
stimuli from the previous experiments, although selection was from
similar categories. This was largely dictated by the success of
definitions in eliciting the intended name. Definitions generally
included the superordinate term and a description of the object (e.g.
skirt - item of clothing for women which hangs from the waist). Where
possible, the object was defined by the use of functional features, but
on some occasions, definitions included visual features. A list of
potential prime and filler definitions was pre-tested on a group of 10
participants, and a criterion of 80% correct was adopted. Definitions
which were unsuccessful were altered or replaced. As before, target and
filler pictures were selected from the Snodgrass and Vanderwart (1980)
set.

In all, 30 semantically related prime and target pairs were
prepared, and these were divided into three lists of 10 pairs, which
were rotated across the three semantic priming conditions as before (Lag
3, Lag 1, unprimed control). For the repetition priming conditions, a
separate set of 18 prime and target pairs were selected (from similar
semantic categories), such that the prime successfully elicited the
target picture name. These were divided into three lists of six prime
and target pairs, which were also rotated across the repetition priming
conditions (Lag 3, Lag 1, unprimed control). A full list of prime
definitions and target pictures is given in the Appendix.

Procedure

Definitions and pictures were presented as before in the centre of
a window on the screen of a Macintosh computer. Definitions occupied
between two and three lines, and the whole definition was presented at
once. The participants were asked to retrieve the object name, either
from a definition, or a picture, as quickly but as accurately as they
could. The stimulus remained on the screen until the response, and then
the screen remained blank for 3 seconds. Following this, a fixation
symbol appeared for one second, which reminded participants as to the
nature of the next stimulus; a picture was preceded by the symbol [ ],
and a definition was preceded by a series of dashes: - - -. Participants
received four practice trials (12 stimuli) before the experimental
trials.

The sequences of four stimuli were randomized separately for each
participant. Naming latencies, measured to the nearest ins, were
automatically recorded, while the experimenter noted any errors,
hesitations or equipment failures.

Results

The data were variable, with a few latencies even longer than 3
seconds. Reciprocal transformations were used to minimize the influence
of outlier participants. In the calculation of participant means, target
latencies above 3 seconds were excluded, providing they were more than 2
standard deviations (SD) above a participant's mean. This led to
the exclusion of only six scores. As before, results of analysis on
means and transformations will only be reported where these differ from
the results of median analysis.

Median participant response latencies were calculated for all six
conditions, after exclusion of errors and machine failures as before.
The means of medians (and percentage error rates) are shown in Table 2.
One participant's median latency for the Lag 1 semantic priming
condition was identified as an extreme point, using exploratory data
analysis techniques, substantially influencing the mean value, and Table
2 shows the means for the semantic priming conditions excluding this
participant's data. Note though that analyses are conducted both
with and without this participant's response.

It is clear that the pattern of data for repetition priming and
semantic priming conditions are different. Although it was nor the
original intention to analyse these data together, an initial analysis
which included type of priming as a factor (semantic or repetition) in
addition to prime condition (Lag 3, Lag 1 or unprimed) indicated a
significant interaction between the two factors, F(2, 70) = 3.28, p
[less than] .05 MSerror = 30138).

Semantic priming

The pattern of data for the semantic priming conditions does show
that the interference from related primes is less marked for the Lag 1
condition than for the Lag 3 condition. However, the planned comparison
between these two conditions only approached significance in the items
analysis (by participants, t(35) = 0.10, p [greater than] .10; by items,
t(27) = 1.58, p = .06, one-tailed). Two items (hen and peach) were
excluded from the analysis because of high error rates. However,
comparisons against the control condition, using Dunnett's test,
indicated that the Lag 3 latencies were significantly longer than
latencies in the control condition, for both participant and item
analyses, p [less than] .05, one-tailed test). Latencies in the Lag 1
condition did not differ from the control condition (p [less than] .05).
These same results were obtained when reciprocal transformations were
used, or when the participant with extreme Lag 1 latencies was removed
from the analysis.

Using the Friedman analysis, no difference was found in the
prime-related error rate across conditions, [[chi].sup.2] = 0.54, p
[less than] .05. Similarly, there was no difference in nonprime-related
errors, [[chi].sup.2](2) = .09, p [less than] .05.

Repetition priming

Although the means in Table 2 show that target pictures were named
more quickly in the two prime conditions than in the control condition,
comparisons of median latencies, using Dunnett's test, indicated no
significant differences, either by participants or by items (p [less
than] .05, one-tailed). The planned comparison of Lag 1 latencies
against Lag 3 latencies was also not significant, by participants, t(35)
= 1.34, p [less than] .05, and by items, t(17) = 0.83, p [less than]
.05.

Analysis of participants' mean latencies, however, did show
that latencies were faster in the Lag 1 condition than in the control
condition (using Dunnett's test, p [less than] .05, for both
participants and items analyses (one-tailed)). Using a reciprocal
transformation, comparisons of Lag 3 mean latencies against the control
approached significance (p [less than] .10 (one-tailed)) for both items
and participants.

Analysis of errors (total errors) indicated no significant
difference between Lag 1 and Lag 3 conditions, t(35) = 0.85, p [less
than] .05. Comparisons against the control conditions, using
Dunnett's test, resulted in a significant difference between the
Lag 1 and control condition (p [less than] .01 (one-tailed)). The
difference between Lag 3 and control condition just failed to reach
significance at the 5% level (p [less than] .10, one-tailed).

Discussion

The data from Expt 3 were noisy, and effects were not as clear-cut
as in the previous two experiments. There may be three reasons for this.
First, participants may have needed more practice at retrieving names
from definitions, and switching between picture and definition trials.
Second, the number of trials per cell was also reduced for the
repetition priming conditions. Finally, the inclusion of both repetition
and interference trials may have tempered effects (Neumann, 2001),
although this is difficult to assess from this single experiment.
Nevertheless, the pattern of data across conditions allows us to draw
some preliminary conclusions concerning the issue of self-inhibitory
mechanisms during picture name retrieval.

We argued that if there is a brief inhibitory mechanism operating
during picture naming, then Lag 3 related primes should interfere with
retrieving the names of target pictures, but Lag 1 primes should not.
This pattern of data was evident; target latencies in the semantic
priming Lag 3 condition were significantly longer than in the control
condition, while there was no difference between Lag 1 and control
target latencies. We discuss other aspects of the semantic priming
results shortly, but the pattern of data is atleast consistent with the
suggestion that primes in Lag 1 condition are temporarily inhibited, so
that they do not interfere with retrieving target names. Although we
cannot rule out the possibility that the inclusion of repetition trials
may have had some influence on processing in other conditions, certainly
the data do not suggest that inhibitory mechanisms have simply been
abandoned, or that participants made consistent strategic use of the
prime throughout the experiment (either in an anti cipatory or an
episodic fashion). Were this the case, the semantic priming data would
have shown specific costs in the Lag 1 condition.

Turning now to the repetition priming data, we predicted that if
the inferred inhibition operates on a self-inhibitory basis, then
facilitatory priming effects should be stronger for Lag 3 primes than
for Lag 1 primes. This pattern of results was not evident. Target
latencies in the Lag 1 and Lag 3 conditions did not differ
significantly, and naming latencies were in fact slightly faster in the
Lag 1 condition. Latencies in the Lag 1 repetition priming condition
were significantly faster than the control condition when the analysis
was conducted on means, suggesting that effects may have been restricted
to slower responses. The comparison of Lag 3 and control condition mean
target latencies only approached significance using Dunnett's test.
Analyses of errors were consistent with the latency data; there were
significantly less errors in the Lag 1 condition than in the control
condition, and the difference between Lag 3 and control conditions just
failed to reach significance using Dunnett's test. Therefore, the
repetition priming data show some indication of facilitatory priming,
but this was only really evident in the Lag 1 condition. This is not
consistent with the suggestion that primes in the semantic and
repetition priming Lag 1 condition undergo a brief suppression as a
result of an automatic self-inhibitory mechanism. If the lack of
interference of Lag 1 primes in the semantic conditions does reflect
temporary inhibition, then the data suggest that it may be accomplished
by a method other than self-inhibition. Inhibition appears to be
restricted to trials where a prime is followed by a competing target
(semantically related), suggesting that inhibition occurs as a result of
processing the competitor target. A possible candidate mechanism is that
of lateral inhibition from the activated target representations to the
prime representations. However, if this occurs, any such inhibition must
be both fast acting, and must be more strongly directed to the
representations of a very recently named competitor (i.e. the
semantically related Lag 1 prime), than to a competitor named three
trials earlier. Following through the argument for lateral inhibition;
in the case of the repetition priming trials, there is no related target
to exert an inhibitory influence on the Lag 1 prime representations, and
so some facilitation is evident as a result of the repeated processing.

One worrying aspect of the repetition data is that facilitation
priming effects in the Lag 3 condition did not reach statistical
significance. Durso and Johnson (1979) did not find that facilitatory
effects reduced markedly over 2 to 8 lags, and Wheeldon and Monsell
(1992) found repetition priming from retrieving object names from
definitions several trials earlier. We need therefore to consider
whether the higher proportion of non-repetition trials actually biased
participants' expectancies against repetition, overriding to some
extent any automatic component to the facilitatory priming (Neumann,
2001). An experiment altering the proportion of semantic and repetition
priming trials could address this possibility directly. However, any
argument for a bias against repetition in the present experiment needs
to accommodate the finding that facilitatory priming was mainly evident
in the Lag 1 condition. Either it is the case that any bias against
repetition is stronger for Lag 3 repetition (which seems unlikely, and
does not fit the Lag 3 semantic interference effects), or else we need
to acknowledge that, despite any such bias, the data are still
inconsistent with the suggestion that representations undergo a brief
period of self-inhibition.

We earlier argued that the semantic priming data are not consistent
with routine episodic evaluation of the prime as a candidate target
response on every single trial. However, it does remain a possibility
that the Lag 1 repetition priming effect is due to strategic episodic
use of the prime which is restricted mainly to the repetition priming
trials. This would imply that participants only use the prime after a
relatively late stage of processing the target, when they are reasonably
confident that prime and target match. For example, participants could
fully process the target semantically, and only then, if this matched
the prime semantic specification, by-pass aspects of target name
retrieval by simply re-stating the prime name from the immediately
preceding trial. This might lead to the occasional error or increased
latency when prime and target resembled each other very closely in the
semantic priming conditions. There is some indication of this in the
slightly raised prime-related error rate for Lag 1 semantic priming
condition; the error rate is actually higher than the control, and this
is due largely to one set of highly similar prime and target objects
(hen misnamed as prime cockerel).

In summary, the semantic priming data from Expt 3 show a pattern
which is generally consistent with the existence of a brief inhibitory
effect after name retrieval. The pattern of data from repetition trials
is not consistent with any such inhibitory effect operating as a result
of a self-inhibitory mechanism. There was no indication of any specific
difficulty in immediately retrieving the same name, and in fact
facilitatory priming was mainly indicated only in the immediate
repetition trials. The patterns of semantic and repetition priming data,
taken together, do not indicate any clear-cut bias either towards or
against repetition, though we cannot rule out the possibility that the
inclusion of companion conditions may have to some extent influenced
interference or facilitatory effects. Similarly, the overall pattern of
data suggests that there is no systematic episodic use of the prime. But
again, we cannot eliminate the possibility that strategic episodic use
of the prime response in repetition trials on ly may have allowed
participants to by-pass selfinhibited lexical representations.

GENERAL DISCUSSION

Earlier research in our laboratory has shown that when participants
name semantically related pictures under speeded naming instructions,
they make errors which relate to earlier named pictures but not the
immediately preceding picture (Vitkovitch et at., 1996; Vitkovitch &
Rutter, 2000). We have interpreted this as evidence that sequential
picture naming involves a brief suppression of the just-named picture
representations. Two of the three experiments reported here have
examined the relationship between the apparent inhibition of one naming
trial, and naming latencies on the next trial. Experiments 1 and 2 used
exactly the same design and stimuli, and complemented each other by
providing error data and latency data which showed that there was no
interference from related primes when they were presented immediately
before a target picture, although interference was evident from a prime
presented three trials earlier. The error data from Expt 1 are therefore
consistent with our own earlier work, and are usef ul because we are now
able to show negative error priming across two different designs -- one
in which naturally occurring errors are analysed as a function of lag
between error and earlier trial, and the other where the lag between
prime and target stimuli is actually manipulated.

Yet further support for reduced interference effects from Lag 1
primes comes from the paradigm used in Expt 3. Here, primes in Lag 1 or
Lag 3 conditions were presented as definitions, from which the object
name had to be retrieved. Target naming latencies were longer in the Lag
3 related condition than the control condition. There was no significant
difference between Lag 1 and control conditions.

In summary, Expts 1, 2 and 3 all show reduced interference effects
from Lag 1 related primes relative to Lag 3 related primes. We have
interpreted this as evidence for a brief inhibitory effect, but we
referred to another possible explanation of the data. Wheeldon and
Monsell (1994), in their definition priming experiment, suggested that a
facilitatory priming effect in the Lag 1 condition counteracted the
competitor priming effect, though the evidence they present in favour of
this is indirect. We argued against this in Expts 1 and 2, because the
data did show a specific reduction of prime-related errors in particular
-- other errors which reflected the names of exemplars from the same
semantic category were not significantly reduced in the Lag 1 condition.
Furthermore, in our work on the analysis of naturally occurring errors
as a function of lag between error and earlier trial (Vickovitch et al.,
1996; Vitkovitch & Rutter, 2000), we do not have this ambiguity in
interpretation. In this paradigm, we are ab le to show that a particular
trial might be subject to interference from a response three or four
trials earlier, but at the same time there is specifically no
interference from the immediately preceding trial. This pattern of data
cannot be accounted for by facilitatory priming from the immediately
preceding trial. Therefore, we are confident that an inhibitory account
fits the picture naming data in Expts 1 and 2 more comfortably than an
account which includes the operation of dual processes of competitor and
facilitatory priming. In Expt 3, which was most similar to Wheeldon and
Monsell's (1994) study, our arguments for ruling our faciliratory
priming are perhaps less convincing, though again the error data are not
consistent with such an account. Retrieving an object name from a
definition rather than a picture is quite likely to encourage a richer
semantic processing than retrieval of a name from a picture, and it
remains a possibility that facilirarory priming might be occurring in
Expt 3 but not in Exp ts 1 and 2. On the grounds of parsimony, however,
we prefer an explanation which encompasses the similar results from the
all three experiments and an explanation which is based on the operation
of a single process rather than two opposing processes. On this basis,
then, we would argue that there is little or no interference from primes
which are presented immediately before a semantically related target
because the prime representations undergo a brief period of inhibition.
Such a conclusion fits well with other research on inhibitory effects in
cognition, and in particular both the data and interpretations parallel
findings by Campbell and colleagues in their study of number fact
retrieval (Campbell, 1990; Campbell & Clark, 1989).

Experiment 3 also included repetition priming trials to allow a
preliminary investigation of whether any such inhibition in sequential
picture naming is the result of a self-inhibitory mechanism. We
predicted that facilitatory priming should be stronger in the Lag 3
repetition condition than the Lag 1 condition if prime representations
suppressed themselves very briefly. We found no evidence in this
experiment that there was a specific difficulty in immediately
re-activating prime representations; evidence for facilitatory priming
was most apparent when the repetition trials were in immediate
succession (Lag 1 condition). This suggests that the inhibition we have
argued for in the semantic priming Lag 1 trials may occur as a result of
another mechanism, such as lateral inhibition from the target
representations to the competing related prime representations. The
results from the present experiments cannot address the issue of
alternative mechanisms of inhibition directly, although we did note that
any latera l inhibition from the target to the prime representations
must be both immediate and most potently directed to the strongest
competitor.

There are several provisos to the conclusion that a self-inhibitory
mechanism does not account for the reduced Lag 1 semantic interference
effects. First, repetition priming effects were not strong, and were
barely evident in the Lag 3 conditions. We noted a number of possible
reasons for this, including the possibility that the inclusion of
semantic priming trials may have tempered repetition effects. Second, an
episodic retrieval account would fit data which showed stronger
immediate repetition priming effects than for earlier trials. We are
confident that participants are not routinely evaluating the Lag 1 prime
as a candidate response to the target, because such a strategy would
lead to specific costs in the Lag 1 semantic priming conditions.
However, participants might restrict themselves to using the prime
response only after they are confident that the target and prime match,
and if so, they may by-pass lexical/ phonological representations which
have been self-inhibited. Some accounts of language pro duction do
include self-inhibitory mechanisms which are directed at phonological
representations (e.g. Dell & O'Seaghdha, 1991; Mackay, 1987).
In other work, we are addressing the locus of inhibition during picture
naming, and it would clearly be useful to combine this with the current
work on the mechanism of inhibition.

In conclusion, the experiments reported here have provided data
consistent with earlier work on inhibitory effects during sequential
object naming, and have allowed a preliminary investigation into the
mechanism of this inhibition. The data from the repetition priming
conditions in Expt 3 show that participants do not have difficulty in
immediately re-activating a just-named object, despite data in the same
experiment which suggests that under other conditions, just-named
objects are briefly inhibited. Although the data are not consistent with
suppression occurring as a result of self-inhibitory mechanisms, we
acknowledge that there is more than one interpretation of the repetition
priming data, and that further work is required before such a mechanism
is ruled out.

Acknowledgement

This work was supported by an ESRC grant awarded to the first
author (R000221593).

(*.) Requests for reprints should be addressed to Dr Melanie
Vitkovitch, Department of Psychology, University of East London, Romford
Road, London E15 412, UK (e-mail: m.vitkoviech@uel.ac.uk).